The field of the invention relates to cooling systems for internal combustion engines, in particular for use in automobiles.
In a liquid cooled internal combustion engine, a liquid coolant is circulated from a radiator through a block jacket in thermal communication with the cylinder block, then into a head jacket in thermal communication with the engine head, and then back into the radiator. The liquid coolant is circulated by a centrifugal pump, mounted at the front of the engine block, which has a pump impeller positioned either within the block jacket or within a casing forming an extension of the block jacket. Mechanical power is transmitted from the engine crankshaft to the impeller shaft by a belt and associated pulleys. Various water seals, bushings and bearings are required to both position and seal the impeller shaft.
In liquid circulation systems, other than automobile cooling systems, it is known to couple an electric motor to the impeller shaft of a centrifugal pump via a magnetic clutch. More specifically, the impeller is separated from the electric motor by a water-tight membrane having nonmagnetic properties. Permanent magnets are connected to both the motor shaft and the impeller shaft such that the impeller rotates in response to movement of the motor shaft. Examples of magnetic clutches are described in U.S. Pat. Nos. 3,411,450; 3,465,681; 3,306,221; 3,520,642; 3,647,314; 3,723,029; 3,802,804; 3,826,938; 3,932,068; 3,938,914; 4,013,384; 4,135,863; 4,226,574; and 4,308,994.
Publication of German patent application OLS No. 1,538,894 shows the adaption of an impeller shaft, having permanent magnets attached thereto, for use as the axial rotor of a DC motor. More specifically, permanent magnets are shown connected to the impeller shaft and separated from the motor coils by a membrane. It appears that this configuration combines both the DC motor and magnetic clutch as a single integral unit.
It is believed that the above-described magnetically coupled pumps have not been used in automobile coolings systems due to at least the following problems. First, there is inherent inefficiency in generating electrical power from the engine through an alternator, and then converting the electrical power back into mechanical power via an electric motor for driving the impeller. Second, the torque output of the above-described magnetically coupled pumps may be inadequate for use in an automobile cooling system.
A problem with all current approaches to automobile cooling systems is that liquid coolant enters the block jacket first and then, after the liquid coolant has received heat transfer from the engine block, the coolant enters the head jacket. Accordingly, the cylinder head may not be cooled sufficiently to prevent engine operating abnormalities, such as knocking and pre-ignition. Similiarly, the engine block may be overcooled thereby reducing lubricating efficiency in the engine block. The inventors herein have recognized that these engine operating abnormalities may be reduced by reversing the conventional flow of coolant such that the cylinder head is cooled first. In addition, by cooling the engine block with coolant which has been heated by the cylinder head, more efficient lubrication will be achieved in the engine block.
The inventors herein have recognized that another problem with automobile cooling systems is that the flow rate of liquid coolant is designed for worst case engine operation such as during heavy load operation. Thus, during normal engine operating conditions, an excess flow of coolant results in operating temperatures which are too low for efficient operation. In addition, driving the coolant pump at a higher speed than is required during normal engine operating conditions results in a considerable waste of engine output power.